The present invention relates to an electronic device for monitoring the weft or filling thread insertion on a gripper shuttle weaving machine provided with a color changing mechanism which transfers one of a plurality of weft threads drawn off fixedly mounted supply spools to a projectile which is ready for insertion into the weaving shed.
In its more specific aspects the gripper shuttle loom for which the electronic monitoring device is provided is of the type comprising a substantially cylindrical shell having an interior surface and rotatably mounted on a changer shaft and provided with groove in substantially parallel relationship to the changer shaft. Each groove receives a retract rod bearing a weft clamp for transferring, at a transfer point, one at a time of a multiplicity of threads drawn from supply bobbins, to a gripper shuttle ready for insertion into the weaving shed.
Such gripper shuttle loom working with freely propelled gripper shuttles or projectiles and a colour changing mechanism of the aforementioned type are illustrated in FIGS. 1, 2, 6 and 7 of U.S. Pat. No. 2,817,367. However, no weft thread monitoring device is provided on this known gripper shuttle loom.
In German Pat. No. 1,760,787 there is described a mechanically operating weft thread monitor on a gripper shuttle weaving machine equipped with a color changing device. With this known embodiment the weft or filling threads are drawn from supply spools located outside the weaving machine, and inserted into the weaving shed by projectiles or gripper shuttles which are picked off by a picking mechanism. Mechanical feelers are provided each of which senses one of the weft threads prior to entering the picking mechanism. The ones of the feelers which are adjoined to weft threads not ready to be inserted with the next shot remain idle.
In U.S. Pat. No. 4,051,871 there is shown an electronic device for monitoring weft yarn insertion on shuttleless looms, which device comprises a plurality, e.g. eight, transducers each to be activated by a weft yarn to be inserted. Photoelectrical, electromagnetic, capacitive, and in particular piezoelectrical transducers may be provided. A switch is individually associated with each transducer for being closed and activating the transducer upon insertion of the weft yarn associated thereto.
Generally weft thread monitors serve for stopping the weaving machine and activating an indicator in the event of an incorrect weft insertion and particularly weft break or rupture.
In addition to said known monitoring devices arranged at the picking side of the weaving machine, others are known which scan or monitor the weft thread already inserted in the shed on the catching side of a gripper shuttle weaving machine, that means in the last phase of the insertion. However, the present invention refers to monitors located at the picking side rather than catching side, such as to make possible monitoring of the weft or filling thread during the entire interval of weft insertion.
The known multi-color monitoring devices located on the picking side make use of a multiplicity of sensors or transducers each of which is associated with one of the weft threads to be inserted. Accordingly, the outlay for the production, assembly and continuous monitoring is substantial.
In order to avoid such an outlay, German Pat. No. 2,212,907 provides for an electronic thread monitor for gripper shuttle weaving machines comprising a single piezoelectrical signal generator or sensor mounted between a thread gripping point and the selvedge. A swivel arm is adjoined to each weft thread for transferring to the gripper the one thread which is to be inserted into the shed. Upon seizure of the thread by the gripper and return of the swivel arm to the starting position thereof, a rotatable thread control pin leads the weft yarn in contact with the signal generator. This electronic weft yarn monitor is relatively simply constructed, however it may be used only on gripper or rapier weaving machines of a rather specialized type rather than conventional gripper shuttle machines.